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InterHam Advanced Waveform

Introduction

An open source waveform to provide time division multiple access (TDMA) and frequency division multiple access (FDMA) capabilities on top of current Wi-Fi technology. Currently the HamWAN project uses a proprietary version of Wi-Fi with TDMA. The goal of InterHam is to provide a protocol available to anyone, including commercial vendors, to implement. Currently the project is in the research and development phase.

Technologies Used

TDMA provides more efficient use of limited radio spectrum by assigning clients chunks of time (time slots) on the network in which they can freely transmit. This eliminates the overhead of requesting permission to transmit and waiting for a response, along with preventing another client from trying to request at the same time, causing neither to get a response.

FDMA also provides more efficient use of spectrum by dividing a channel up into smaller pieces (subchannels) in which multiple clients can transmit at the same time, including the ability to avoid parts of the spectrum occupied by interference. By dynamically allocating subchannels to clients it can scale based on bandwidth and latency requirements of clients currently on the network. For example, under heavy network load, small subchannels can be dedicated to certain clients (and further divided by TDMA) to ensure low latency connections for low bandwidth services such as voice-over-IP (VoIP). Another benefit from dynamic subchannel allocation is allowing multiple networks squeezed together to avoid stepping on each other by fairly dividing up available spectrum among the overlapping networks.

Strong subchannel filters reduce the out-of-band noise from a subchannel, allowing tighter grouping for more efficient bandwidth usage.

Current Status

The design is currently being developed in GNU Radio. This will allow testing of the waveform in varying simulated conditions to optimize it. Source code will be made publicly available.